Monday, April 18, 2016

The ciphers of Czechoslovakia’s government in exile

At the end of
the First World War the multiethnic Austro-Hungarian Empire collapsed
and out of its ruins emerged several new countries. One of these was Czechoslovakia,
containing the Czech areas of Bohemia and Moravia together with Slovakia and
Carpathian Ruthenia in the east.

In the interwar period Czechoslovakia followed a foreign policy supportive of
France and was part of the Little Entente. The
country had a stable democracy and its industrial resources were large (based
on the Skoda works)
for such a small country. However there were two important problems affecting
Czech national security. On the one hand the rise of Nazi Germany and its
rearmament was a clear security threat. At the same time there were serious
problems with the German and Slovak minorities that resented Czech
rule.

Czechoslovakia contained a large number of minorities that were dissatisfied
with the ruling Czech establishment. Especially the German
minority made up roughly 23% of the population (according to the 1921
census) and a large part of it was concentrated in the border with
Germany called Sudetenland.
Many of the Sudeten Germans wanted for their areas to be unified with Germany
and in the 1930’s Hitler’s Germany supported the demands of the Sudeten
German Party. These claims were rejected by the Czech government of Edvard
Beneš and as the Czech crisis threatened Europe with a new war a conference
took place in Munich
between the governments of Germany, Italy, Britain and France.

Without
support from Britain and France the Czech government was forced to cede the
Sudeten territories to Germany and also lost other disputed areas to Hungary
and Poland. Even though Germany had succeeded in absorbing the Sudeten areas
and in weakening Czechoslovakia that did not stop Hitler’s offensive plans and
in March 1939 German troops invaded and occupied the rest of the country. From
then on the country was ruled by Germany and special attention was given to its
heavy industry which produced weapons for the German armed forces.

During the
war the Czechoslovak
Government in Exile, headed by Beneš, was based in London and had regular
communications with the Czech resistance and with its diplomatic missions and
intelligence service stations abroad. In order to protect these communications
several cryptosystems were used by the Czech crypto department.

Information
on these systems is available from books and articles written recently:

Cipher ‘Rimska devat’
(letter to figure substitution followed by additive encipherment, repeating
additive created from a passphrase)

Cipher ‘Rimska desat’
(letter to figure substitution followed by transposition then additive
encipherment, repeating additive created from a passphrase, passphrase is also
used to limit the cells of the transposition table)

The Czech
resistance movement and the Czech intelligence service caused serious problems
for the German authorities with their most audacious operation being the
assassination of Reinhard
Heydrich, protector of Bohemia and Moravia and former head of the
Reich Main Security Office. However after this episode the Germans took many
security measures and were generally able to keep the resistance activities
under control. Keeping the Czech areas pacified was particularly important
since Czechoslovakia had a developed heavy industry sector which produced
weapons for the German armed forces.

In their
counterintelligence operations the Germans benefitted from having the ability
to read a substantial amount of the traffic exchanged between the Czech IS in
Britain and the Czech resistance in the occupied territories. This case has
been covered in detail in Svetova
Revoluce and the codes of the Czechoslovak resistance.

Report on
the compromise of the communications of the government in exile

After the end
of WWII it seems that the Czechoslovak authorities learned from POW
interrogations about the compromise of their ciphers. Karol
Cigáň, who worked in the Defense Ministry’s cipher department, summarized
some of this information in a report written in 1989.

The report ‘Dopady lúštenia šifrovacieho systému čs.
londýnskeho MNO z rokov 1940-1945 na domáci odboj’, can be found in the
archive of the Museum of the Slovak National
Uprising in Banská Bystrica

and in the Central
Military Archive at Prague.

In the report
Cigan analyzed the Czechoslovak STP cipher and found it insecure. In addition
he proved the compromise of Czechoslovak ciphers by examining reports from the
office of the high ranking SS official Karl Hermann Frank.

A report from
November 1944 had a summary of Funkwabwehr (Radio Defense) operations and it
said that during the previous month 8 radio links, whose cipher procedures
could be solved, were kept under observation. Of special interest was traffic
between the Protectorate and London regarding the preparations for the uprising.

In the month
of October a total of 488 messages were solved and 8 cipher keys derived for
the STP cipher.

In pages
37-41 Cigan directly compared the Funkawbehr decodes with some of the
Czechoslovak telegrams found in the country’s national archives.

The author’s
conclusion was that the use of insecure ciphers during wartime played an
important role in undermining the operations of the Czechoslovak resistance movement
and these events should be acknowledged by the country’s historians.

Acknowledgments: I have to thank Jozef Krajcovic for his help in
locating the report ‘Dopady lúštenia
šifrovacieho systému čs. londýnskeho MNO z rokov 1940-1945 na domáci odboj’
and Štefan Porubský for informing me of the
articles from Crypto World.